The present invention pertains to a process for regulating the air temperature in an incubator accommodating a patient and more particularly to a hybrid device combining essentially an incubator and a heat radiation source.
An incubator that is part of a so-called hybrid comprises essentially an incubator and a heat radiation source and as a result combines the advantages of two types of devices. A comfortable climate can be reliably established for a patient with a closed incubator, and a heat radiation source above an open care unit facilitates the access to the patient for care and supply procedures. The function of hybrids can be changed from one type of device to the other or vice versa, i.e., from a closed incubator to an open care unit, with little effort. Closed incubators produce the necessary climate usually by means of convection heating and a moisture evaporator, and open care units are heated by means of heat radiation sources. The problem arising in connection with changing the function of the hybrid from one type of device to the other is that the air temperature in the hybrid cannot be reliably maintained for the patient. When the incubator is opened the heat radiation source is used instead of the convection heating, or vice versa. When the incubator is closed, the heat radiation source is switched off and the convection heating is switched on instead. The temperature in the incubator drops greatly during a certain period in both cases causing the cooling of the patient in the meantime.
A hybrid and a process for maintaining the body temperature of a patient during a changeover from one type of device to the other are described in U.S. Pat. No. 5,817,003. This goal is accomplished only insufficiently by the design of the hybrid and with the process used therein for the enmeshed regulation of the output of the convection heater and the heat radiation source. The changeover in a hybrid from the device type of an open care unit to the device type of a closed incubator therefore leads to irregular fluctuations in the patient""s body temperature. At equal air temperature, a heat radiation source causes a higher temperature on the skin surface of a patient than a convection heater. If, e.g., the temperature on the skin surface of the patient is now used to determine his body temperature, different conversion methods must be used in the two cases. If this difference is not taken into account, the body temperature will be inevitably incorrect. At the time of the changeover from the heat radiation source of the open care unit to the convection heating of the closed incubator, the heat radiation source is lowered together with the incubator hood to close the incubator. However, the heat radiation source must have cooled sufficiently before it comes close to the patient in this manner in order to prevent burning the patient due to the unintended contact. Since the infrared radiation sources used for this purpose in practice frequently have surface temperatures of a few hundred degrees, there also is a fire hazard at increased oxygen concentration or in the case of the use of disinfectants containing alcohol. The transition time between the two device types is therefore always a few minutes in order to ensure that the infrared radiation source will have cooled sufficiently at the time of the transition from the open care unit to the closed incubator before it reaches the vicinity of the patient and conversely, the infrared radiation source already has a sufficient distance from the patient before it heats up at the time of the transition from the closed incubator to the open care unit. The air temperature in the incubator of the hybrid can be maintained only insufficiently during this transition time, so that a patient located herein will cool off. Furthermore, it may be necessary to open the hood of an incubator immediately. Preheating by switching on the heat radiation source in advance is no longer possible. The convection heating of the opened incubator is already switched off and the heat radiation source is not heated up, so that the patient will cool off.
To avoid the risk of burn for the patient or a fire hazard, the infrared radiation source in a hybrid can be covered during the transition time between the two types of device with an automatically opening and closing flap. The transition times during the changeover between the two types of device, during which the body temperature of the patient decreases, are thus shortened. However, this requires complicated technical measures and may lead to an alleviation, but not to the elimination of the problem of the insufficient regulation of the air temperature for maintaining the patient""s body temperature in the hybrid.
The object of the present invention is to provide a process for regulating the air temperature in an incubator for a patient, which guarantees that the body temperature is also maintained during the changeover between the different types of device.
According to the invention a process is provided for regulating the air temperature in an incubator which accommodates a patient, can be closed, is transparent to heat radiation and is exposed to the radiation of a heat radiation source. An air temperature sensor is provided in the incubator. An evaluating and control unit evaluates the signals received from the air temperature sensor and controls the radiation dose delivered by the heat radiation source. The air temperature sensor receives an actual value TI for the air temperature, which is sent to the evaluating and control unit. The evaluating and control unit compares the actual value TI with an internally preset set point TS, forming the difference TSxe2x88x92TI from the two values and generating a manipulated variable from the difference for the heat radiation source. If TSxe2x88x92TI greater than 0, the radiation dose of the heat radiation source is increased, and if TSxe2x88x92TI less than 0, the radiation dose of the heat radiation source is reduced until TSxe2x88x92TI=0 is reached.
The process for regulating the air temperature in an incubator accommodating a patient uses a heat radiation source, preferably an infrared radiation source, which sends heat radiation to a patient in the incubator. The temperature in the interior of the incubator is measured by the air temperature sensor. This actual value TI for the air temperature is sent to an evaluating and control unit and is compared with an internally preset set point TS for the air temperature in the interior of the incubator. The difference TSxe2x88x92TI is formed from the actual value TI and the set point TS for the air temperature. A manipulated variable for the heat radiation source is generated from the difference TSxe2x88x92TI in such a way that if TSxe2x88x92TI greater than 0, i.e., the actual value is lower than the set point of the air temperature, the radiation dose of the heat radiation source is increased and if TSxe2x88x92TI less than 0, i.e., the actual value is greater than the set point of the air temperature, the radiation dose of the heat radiation source is reduced until TSxe2x88x92TI=0, i.e., the actual value and the set point agree. Incorrect regulation of the patient""s body temperature, which is due to the fact that an air temperature is preset without taking into account whether it was brought about by convection heating or a heat radiation source, is avoided by using only one heat radiation source for the temperature regulation according to the process according to the present invention.
In a preferred embodiment of the present invention, the heat radiation source is installed stationarily in relation to the incubator of the hybrid device for the patient, i.e., there is a constant distance between the heat radiation source and the incubator.
The heat radiation source emits uninterrupted radiation. Undesired long heat-up times, which are due to the fact that when the heat radiation source is switched on, it must first heat up completely before the intended output is reached, are thus avoided. The incubator of the hybrid device for accommodating the patient can be closed with a hood that is transparent to the radiation of the heat radiation source. The climate in the incubator can thus be maintained better in regard to the temperature, the relative humidity and the oxygen content. The air temperature sensor in the interior of the incubator has a screen that is non transparent to the radiation of the heat radiation source. It is ensured as a result that the results of the measurement are not distorted by radiation reaching the air temperature sensor. In the process for regulating the air temperature in the incubator, which accommodates a patient, an actual value for the air temperature, which was measured by the air temperature sensor, is compared with an internally preset set point. In a preferred embodiment of the process, the patient""s body temperature value is first determined with at least one body temperature sensor, e.g., a skin temperature sensor, and is sent to the evaluating and control unit. Actual values for the air temperature in the incubator are received during this time by the air temperature sensor and these are likewise sent to the evaluating and control unit. The evaluating and control unit then presets a set point for the air temperature in such a manner that this corresponds to a desired body temperature value of the patient. Maintenance of a desired body temperature value of the patient is achieved as a result by the regulation of the air temperature. Desired body temperature values are here especially the so-called core temperature, which is determined in the known manner from a skin temperature measurement at the head or on the chest of the patient and the linking by calculation with the ambient temperature of the patient, or the so-called peripheral temperature, which is determined from a skin temperature measurement on the extremities and the linking by calculation with the patient""s ambient temperature.
The relative humidity and the oxygen content in the air in the incubator are also regulated, in particular, besides the regulation of the air temperature. If enrichment with fresh air is performed such that a continuous fresh air supply with bacteria filtering generates a slight overpressure on the order of magnitude ranging from a fraction of one Pascal to a few Pascals in the closed incubator, it is thus ensured that no air will enter from the outside through smaller openings or leaks.
A mattress for the patient, which is equipped with a mattress heater in a preferred embodiment, which is controlled especially by the evaluating and control unit, is located in the incubator. The mattress heater has a temperature control which is operated separately from the air temperature regulation in the incubator.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.